XVIII. The graphic record of the frog's heart=beat. 



/. Appliances. Frog board; a straw or strip of bamboo 20 

 cm. long; a cork about 2 cm. in diameter and height; 

 pins; needles; sealing wax; parchment paper; a kymo- 

 graph, stand and lamp; a chronograph. (See Appendix 

 A- 15.) 



2. Preparation. Use a pithed or a curarized frog. Make a 

 heart lever after the model shown by the demonstrator. 



3. Operation. Open the abdomen of the frog as described 

 under XVII-b 3 and expose the heart. Open the peri- 

 cardium, place some resistant object a cover slip for 

 instance under the ventricle. So adjust the heart 

 lever that the cork foot of the long arm of the lever will 

 rest upon the juncture of the auricles and ventricle. If 

 the weight of the lever seems to be too great for the heart to 

 move easily, the long arm may be made relatively lighter 

 by placing a counterpoise upon the short arm. If the 

 tracing point of the long arm has a sufficient excursion 

 to make a good tracing, bring the kymograph to a posi- 

 tion where the point will lightly touch the carboned 

 surface of the drum. The lever should be nearly tan- 

 gent to the surface of the drum, and so arranged that 

 the rotating surface of the drum turns away from the 

 tracing point of the lever rather than toward it. 



4. Observations. 



(1) Note whether the curve is a simple one or com- 

 posed of a major wave, with crests superimposed 

 upon it. 



(2) In either case closely observe the phases of the 

 heart-cycle and determine the relation of each part 



